Power distribution units (PDUs) for electrical equipment racks such as RETMA racks are becoming highly sophisticated. Once little more than a simple plug-strip, today a PDU may include complex circuitry that can perform such functions as switching any of numerous outlets off and on, receiving commands from and transmitting data to remote power managers, and controlling power sources such as uninterruptible power supplies (UPSs). Such a PDU may include a microprocessor and embedded software and may be accessed through a web browser under control of a remotely-located user. Examples of such PDUs may be found in U.S. Pat. Nos. 7,116,550, 7,137,850, 7,171,461, and 7,196,900, all of which are incorporated herein by this reference.
Physical space that can accommodate a PDU in an equipment rack is at a premium because most of the space in such a rack is occupied by computers and other electronic appliances. Most or all of these appliances draw power from the PDU. Accordingly, PDUs typically are built in long, narrow, tight enclosures that have barely enough room to accommodate one or more power inlets and up to 24 or more power outlets. Such PDUs are often designed with a vertical form factor to facilitate mounting vertically in a back corner area of an equipment rack, out of the way of the appliances in the rack but accessible from the rear of the rack so that the appliances can readily be plugged into and unplugged from the outlets.
In general, PDU housings have not expanded despite the addition of more complex circuitry that gives the PDUs more capabilities. However, this circuitry generates heat, and as more such circuitry is added into the confined space of a PDU housing, dissipating this heat has become a significant problem.
Adding to the heat dissipation problem has been the trend to install increasingly-complex computers and other appliances, and more of them, in electrical equipment racks. This has had the effect of generating more heat within the rack, making more demands on the PDU and thereby increasing the amount of heat generated by circuitry within the PDU, and reducing the volume of air in the rack that can dissipate that heat. The combination of more heat generated in a confined space within the PDU, more heat generated by the appliances in the rack, and less air space in the rack, has led to great difficulty in keeping the internal temperatures within PDUs within safe limits.
The general problem of thermal management in equipment racks has been recognized, and various methods and devices have been proposed for cooling computers, computer power supplies, and other appliances in an equipment rack. By way of example, in U.S. Pat. No. 7,173,821 issued to Coglitore, it is proposed to install various appliances back-to-back in a rack with an overhead power supply, with cooling air to flow between the appliances, and to locate a central power supply in a rack by itself with a dedicated cooling system.